The present invention is directed, in general, to power conversion and, more specifically, to a snubber circuit for a bidirectional power converter.
A power converter is a power processing circuit that converts an input voltage or current waveform into a specified output voltage or current waveform. A switched-mode power converter is a frequently employed power converter that converts an input voltage into a specified output voltage. A buck power converter is a step-down converter that receives an input voltage and produces an output voltage that, on average, is lower than the input voltage. A boost power converter is a step-up converter that converts the input voltage to an output voltage that is greater than the input voltage. Buck and boost power converters are frequently employed in telecommunications applications as part of a power plant.
While power converters are generally employed to receive power at an input thereof and to transmit the power to a load at an output of the power converter, there are some applications that may require bidirectional power transmission. In battery back-up applications, for example, a battery is frequently used to provide back-up power in the case of a power outage. A power converter may, in a normal mode of operation, be required to provide power of a specific voltage to charge the battery. Then, during a power outage, the power converter may be required to convert power from the battery to power of another voltage as may be required for powering the load equipment.
A non-isolated bidirectional power converter that may be employed in such applications generally includes an energy storage device (e.g., an inductor) and a first power switch series-coupled across a battery. A second power switch may then be coupled to a node between the energy storage device and the first power switch. Depending on the mode of operation, the bidirectional power converter may be employed as a buck power converter or as a boost converter. When operating as a buck power converter, the second power switch is employed to regulate the voltage provided to the battery while the first power switch is employed as a rectifying switch. Alternatively, when operating as a boost power converter, the first power switch is employed to charge the boost inductor, while the second power switch is employed as a rectifying switch.
Analogous to all types of power converters, the bidirectional power converter is subject to inefficiencies that impair its overall performance. The first and second power switches [e.g., metal-oxide semiconductor field-effect transistors (MOSFETs)] are subject to losses when substantial voltage and current are simultaneously imposed thereon during the transition periods thereof. The losses associated with the first and second power switches increase linearly as the switching frequency of the bidirectional power converter increases. Therefore, efforts to minimize the losses associated with the first and second power switches will improve the overall efficiency of the bidirectional power converter.
Accordingly, what is needed in the art is snubber circuit that improves the operation of the bidirectional power converter.
To address the above-discussed deficiencies of the prior art, the present invention provides an energy recovery snubber circuit for a bidirectional power converter, a method of operation thereof and a power plant employing the bidirectional power converter. The bidirectional power converter has first and second inputs, an inductor coupled to the first input and a power switch coupled between the inductor and the second input. In one embodiment, the energy recovery snubber circuit includes: (1) a clamping capacitor coupled to the second input; (2) a clamping diode coupled between the clamping capacitor and the first input; and (3) a snubber inductor coupled to a node between the clamping capacitor and the clamping diode.
The present invention introduces, in one aspect, a snubber circuit for a bidirectional power converter. The bidirectional power converter has first and second inputs and an inductor coupled to the first input. The second input is coupled to a voltage source having a leakage inductance associated therewith. The snubber circuit is configured to provide a path for current in the leakage inductance to flow from the second input to the first input.
In another aspect of the present invention, the bidirectional power converter is couplable to an AC bus via a transformer winding and subject to losses resulting from a parasitic inductance of the transformer winding. The snubber circuit is configured to provide a path for current in the parasitic inductance to flow between the transformer winding and the first input. The path may be formed, for example, by a series-coupled clamping capacitor and clamping diode coupled between the transformer winding and the first input. The snubber circuit is further configured to maintain a charge balance of the clamping capacitor by employing a snubber inductor coupled to a node between the clamping capacitor and the clamping diode.
In one embodiment of the present invention, the snubber circuit further includes a second diode series coupled to the snubber inductor. The second diode defines a path for current to flow from the clamping capacitor to the clamping diode.
In one embodiment of the present invention, the bidirectional power converter forms a portion of a power plant having a primary power stage coupled to an AC bus. In this embodiment, the bidirectional power converter is coupled to the primary power stage via the AC bus. The AC bus may further provide inter-connectivity to other parts of the power plant, such as an output stage.
In a related embodiment, the primary power stage includes a startup circuit. The startup circuit may include, for example, a startup inductor coupled across an input of the primary power stage. The startup circuit may further include a startup diode series coupled to the startup inductor.
Alternatively, the startup circuit may include a startup transformer having first and second startup windings. The first startup winding may be coupled across an inductor of the bidirectional power converter, while the second startup winding may be coupled across the input of the primary power stage. The startup circuit may further include a startup diode series coupled to the second startup winding.
In another related embodiment, the primary power stage includes an input capacitor. The startup circuit may be configured to charge the input capacitor when the primary power stage is not converting primary power. The startup circuit may thus enable the primary power stage to develop a voltage across a primary winding thereof, which forms a portion of the AC bus, thereby allowing the bidirectional power converter to provide power to the AC bus.
The foregoing has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art will appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art will also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.